The Interpretation and Meteorological Application of Radar Backscatter Amplitude Ratios at Linear Polarizations

Abstract

Backscatter amplitude ratios are defined for horizontal and vertical polarizations. These new parameters of linear polarization provide not only a coherent interpretation of the magnitude of the cross-correlation function between horizontally and vertically copolarized backscattered signals (?L) but also give new meaning and applications for differential reflectivity (?). In particular, it is demonstrated that ?L and ? can be used to determine the mean and variance of the amplitude ratios. In rain these quantities can be transformed into estimates of the mean and variance of drop axis ratios. This information can potentially improve polarization estimates of rainfall, provided ?L is measured accurately. Amplitude ratios also appear to be useful for investigating melting processes. Measurements indicate the presence of prolate-like scatterers even where ? is greater than unity in some bright bands. It is hypothesized that this scattering from apparent prolates is, at least in part, a result of the wetting of the three-dimensional superstructure of dendritic snowflakes. This same process may also be partially responsible for observations of significant linear depolarization (L) in the bright band. Further investigation of this hypothesis requires laboratory experiments, in situ measurements and observations using linear polarization radar capable of measuring ?, ?L and L simultaneously.